Field of the Invention
The present invention relates to a contact spring constituted by a bare wire and realizing connection between two parts disposed apart from each other in an image forming apparatus, and an image forming apparatus including this contact spring.
Description of the Related Art
An image forming apparatus such as a printer is configured to supply power from a power supply board included in an apparatus body to an imaging unit containing a photosensitive drum, a charger, a developing unit and others via wires. Generally, the power supply board is often disposed at a position away from the imaging unit by a certain distance for reasons of apparatus design. Accordingly, the wires between the power supply board and the imaging unit are supported by a wire support member to prevent hanging of the wire between the power supply board and the imaging unit.
Each of these wires may be constituted by a wire harness including a linear conductive member such as copper, and an insulator such as resin for covering the conductive member. However, the wire harness is generally a high-cost component. Particularly, a wire having a large diameter for receiving a high charging voltage or the like may remarkably raise costs.
For overcoming this problem, there has been proposed a configuration which connects a terminal of a power supply board and a terminal of an imaging unit by using a so-called contact spring. This contact spring is a bare wire such as a stainless steel wire not covered with insulation coating, as a less expensive wire than the wire harness. For example, see JP 2009-110996 A.
When the linear contact spring not covered with insulation coating is routed between the power supply board and the imaging unit, the contact spring is fitted into a groove of an insulating wire support member made of resin or the like, based on the necessity for avoiding short-circuiting with a frame or the like of the apparatus body.
The groove of the wire support member is often bent at a plurality of points in the route between the power supply board and the imaging unit, depending on the positions of the power supply board and the imaging unit. The contact spring is manufactured into a shape having bent portions in a length direction beforehand by bending or other methods in accordance with the shape of the bent groove.
The contact spring is generally manufactured by a process for sequentially bending a linear hard stainless steel wire at each point, i.e., by a process which forms a bent portion by bending the wire at a point and then forms a subsequent bent portion by bending the wire at a subsequent point. In this case, a bending start position corresponding to a bending start of each banded bent portion is easily variable.
More specifically, each bent portion includes a dimensional tolerance. For example, when a bending start position of a second bent portion is shifted by an amount of a dimensional tolerance from a forming position of an initial banded bent portion, a shift by an amount of a dimensional tolerance from a forming position of the second bent portion is further added to the previous shift amount. Similarly, a start position of a third or further bent portion is shifted by a total shift amount of the previous banded bent portions. When shift amounts of respective forming positions are sequentially added in accordance with increase in the number of bent portions, each of the manufactured contact springs may include some variations in the forming positions of the respective bent portions.
Accordingly, even when a bent portion of a certain contact spring is easily fitted by an operator into a bent groove of a wire support member during an assembly step of a manufacture line or the like of an image forming apparatus, a bent portion of another contact spring may be shifted from the position of the tended bent groove due to a variation of the forming position of the bent portion. In this case, a fitting process is difficult to perform.
The operator may continue the process by slightly pulling the contact spring to complete fitting. However, when fitting in this manner is difficult, the operator needs to remove the contact spring from the wire support guide and again fit the contact spring while stopping the process. Alternatively, the operator needs to replace the contact spring with a new contact spring and again fit the new contact spring from the start of fitting. These necessities may lower assembly efficiency.
The foregoing problems occur not only from the structure connecting the power supply board and the imaging unit via the contact spring, but also from a structure connecting other two parts provided on the image forming apparatus.